This invention generally relates to a process control system for mixing and supplying liquids, and deals more particularly with novel improvements in a water fountain mixing and supply system suitable for use in connection with printing press apparatus or the like.
The lithographic printing process produces an inked impression by means of a selectively inked lithographic plate which includes image areas defined by greasy or resinous portions which are adherent to ink. The nonimage areas on the plate, which represent the blank spaces of the printed product, are maintained in a dampened or moist condition during the printing operation by means of a fountain solution which is applied to the plate. The fountain solution, which comprises a carefully proportioned mixture of water and a chemical concentrate such as gum, acid, or alkaline etchant, rejects the ink from non-image areas. Thus, when an ink charged roller is passed over the plate, the ink adheres to the image portions and is rejected by the dampened nonimage areas to reproduce the desired image.
Known dampening systems for applying the fountain solution during the printing operation are usually of the type in which the solution is continuously circulated between a remotely located reservoir of such solution, and various applicator means which are located adjacent to the printing plates. As the fountain solution is consumed during the dampening operation and solution is depleted from the reservoir, fresh quantities of the solution must be mixed and successively transferred to the reservoir to replenish the latter. Prior art dampening systems typically employ a mixing compartment adjacent the reservoir, wherein measured quantities of water and a chemical concentrate are combined in a specific ratio to produce "batches" of the specially formulated solution for subsequent transfer to the reservoir. Because numerous factors tend to affect the fountain solution ratio, such as relative humidity, the type of printing plate being used, the ratio of image to background area, etc., means are normally provided in the dampening system for selectively varying the ratio of chemical concentrate to water with a relatively high degree of precision.
Due to the above mentioned requirements, prior art systems, such as that disclosed in U.S. Pat. No. 3,893,470, devised for mixing and supplying fountain solution have been rather complicated in structure and have resorted to float metering devices, mechanical scale assemblies and the like for providing the portioning and mixing functions. These prior art systems, which are primarily mechanical in their design, are less than completely satisfactory in several respects; the moving mechanical components of these systems are subject to wear with use which, in turn, eventually diminishes the mixing accuracy and repeatability of the system. Moreover, float devices employed in the prior art apparatus sometimes became "stuck" for any of various reasons, and therefore further contributed to the lack of reliability of these previous mechanical type mixing systems.
The present invention represents a significant advancement in the art by providing a fountain solution mixing and supplying apparatus which is not only extremely reliable, but also provides very precise proportioning of the mixed liquid ingredients with consistently repeatable results. According to the present invention, supplies of a chemical concentrate and water and respectively delivered to a mixing tank through a pair of selectively actuated valve means, wherein successive batches of the fountain solution are mixed and then transferred through a third selectively actuated valve means to a reservoir from which the fountain solution is circulated to the printing press for use. An electrical circuit control system controls the operation of each of the valve means and includes electrical means for sensing the quantities of fountain solution in both the mixing tank and the reservoir, and also includes selectively adjustable timing means for correlating the amount of chemical concentrate which is introduced into the mixing tank. After a correlated quantity of the concentrate has been introduced into the tank, the control system functions to add a quantity of water to the mixing tank in order to produce a batch of the fountain solution having the proper concentrate to water ratio. Upon sensing that a prescribed quantity of the fountain solution has been depleted from the reservoir, the control system actuates valve means to effect the transfer of an already mixed batch of the solution from the mixing tank to the reservoir whereby to replenish the latter. As a further feature of the invention, a tank for holding a supply of the chemical concentrate is coupled with the mixing tank through further selectively actuatable valve means to allow delivery of the concentrate to the mixing tank in accordance with the operation of the control system.
The primary object of the invention is to provide a system for mixing and supplying a formulated liquid solution, which employs an electrical control circuit for precisely measuring the quantities of the ingredients comprising the solution, whereby to mix the same in a pre-selected ratio to produce a batch of the formulated solution. In connection with the foregoing object, it is a further object of the invention to provide a system of the mentioned type which correlates the quantity of at least one ingredient used in the batch with a selectively variable time base.
Another object of the invention is to provide a system of the mentioned type wherein electrical sensing means are employed to detect the production of a quantity of the liquid formulation corresponding to a batch thereof.
A further object of the invention is to provide apparatus in a system of the type described which includes a plurality of valve connected liquid containers wherein the valves are responsive to an electrical control system to effect the transfer of liquids therebetween, for mixing and supplying the solution.
Other and further objects of the invention will be made clear or become apparent in the course of the following description of a preferred embodiment of the invention.